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Chapter 3 Telescopes 2017 Pearson Education Inc Units of Chapter 3 Optical Telescopes Telescope Size HighResolution Astronomy Radio Astronomy SpaceBased Astronomy Summary of Chapter 3 ID: 636846

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© 2017 Pearson Education, Inc.Slide2

Chapter 3 Telescopes

© 2017 Pearson Education, Inc.Slide3

Units of Chapter 3

Optical Telescopes

Telescope SizeHigh-Resolution Astronomy

Radio Astronomy

Space-Based Astronomy

Summary of Chapter 3

© 2017 Pearson Education, Inc.Slide4

3.1 Optical Telescopes

Images can be

formed through

reflection or


Reflecting mirror

© 2017 Pearson Education, Inc.Slide5

3.1 Optical Telescopes

Refracting lens

© 2017 Pearson Education, Inc.Slide6

3.1 Optical Telescopes



© 2017 Pearson Education, Inc.Slide7

3.1 Optical Telescopes

Reflecting and refracting telescopes

© 2017 Pearson Education, Inc.Slide8

3.1 Optical Telescopes

Modern telescopes are all reflectors:

Light traveling through lens is refracted differently depending on wavelength.Some light traveling through lens is absorbed.

A large lens can be very heavy and can only be supported at the edge.

A lens needs two optically acceptable surfaces, but a mirror needs



© 2017 Pearson Education, Inc.Slide9

3.1 Optical Telescopes

Types of reflecting telescopes

© 2017 Pearson Education, Inc.Slide10

3.1 Optical Telescopes

Details of the Keck telescope

© 2017 Pearson Education, Inc.Slide11

3.1 Optical Telescopes

Image acquisition

: Charge-coupled devices (CCDs) are electronic devices that can be quickly read out and reset.

© 2017 Pearson Education, Inc.Slide12

3.1 Optical Telescopes

Image processing by computers can sharpen images.

© 2017 Pearson Education, Inc.Slide13

Discovery 3.1: The

Hubble Space Telescope


Hubble Space Telescope

has several instruments.

© 2017 Pearson Education, Inc.Slide14

Discovery 3.1: The

Hubble Space Telescope

Resolution achievable by the

Hubble Space Telescope

© 2017 Pearson Education, Inc.Slide15

3.2 Telescope Size



: Improves

our ability to see

the faintest

parts of this galaxy

Brightness is proportional to


of radius of mirror

The figure, part (b) was

taken with

a telescope twice the size



© 2017 Pearson Education, Inc.Slide16

3.2 Telescope Size

Multiple telescopes: Mauna Kea

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3.2 Telescope Size

The VLT (Very Large Telescope), Atacama, Chile

© 2017 Pearson Education, Inc.Slide18

3.2 Telescope Size

Resolving power

: When better, can distinguish objects that are closer together.

© 2017 Pearson Education, Inc.Slide19

3.2 Telescope Size

Resolution is proportional to wavelength and inversely proportional to telescope size.

© 2017 Pearson Education, Inc.Slide20

3.2 Telescope Size

Effect of improving resolution:

(a) 10

; (b) 1

; (c) 5

; (d) 1

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3.3 High-Resolution Astronomy

Atmospheric blurring due to air movements

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3.3 High-Resolution Astronomy


Put telescopes on mountaintops, especially in deserts.Put telescopes in space.

Use active optics—control mirrors by bending them slightly to correct for atmospheric distortion.

© 2017 Pearson Education, Inc.Slide23

3.4 Radio Astronomy

Radio telescopes

:Similar to optical reflecting telescopesPrime focus

Less sensitive to imperfections (due to longer wavelength); can be made very large

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3.4 Radio Astronomy

Largest radio telescope: 300-m dish at Arecibo

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Longer wavelength means poorer angular resolution.

Advantages of radio astronomy:

Can observe 24 hours a day.Clouds, rain, and snow don’t interfere.

Observations at an

entirely different

frequency get totally

different information.

3.4 Radio Astronomy

© 2017 Pearson Education, Inc.Slide26

3.4 Radio Astronomy




information from


widely separated radio telescopes

as if it

came from

a single dish.

Resolution will be

that of

a dish

whose diameter


largest separation between dishes


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3.4 Radio Astronomy

Interferometry requires preserving the phase relationship between waves over the distance between individual telescopes.

© 2017 Pearson Education, Inc.Slide28

3.4 Radio Astronomy

These telescopes can

get radio images whose resolution is

close to


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3.4 Radio Astronomy

Interferometry can also be done with visible light, but it is much harder due to shorter wavelengths.

© 2017 Pearson Education, Inc.Slide30

3.5 Space-Based Astronomies

Infrared radiation can image where visible radiation is blocked by interstellar matter or atmospheric particles.

© 2017 Pearson Education, Inc.Slide31

3.5 Space-Based Astronomies

Infrared telescopes can also be in space or flown on balloons.

© 2017 Pearson Education, Inc.Slide32

3.5 Space-Based Astronomies

Ultraviolet images

The Cygnus loop supernova remnant


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3.5 Space-Based Astronomies

X-rays and gamma rays will not reflect off mirrors as other wavelengths do; need new techniques.

X-rays will reflect at a very shallow angle and can therefore be focused.

© 2017 Pearson Education, Inc.Slide34

3.5 Space-Based Astronomies

X-ray image of supernova remnant Cassiopeia A

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3.5 Space-Based Astronomies

Gamma rays are the most high-energy radiation we can detect. This supernova remnant would be nearly invisible without the Fermi satellite and its gamma-ray detector.

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3.5 Space-Based Astronomies

Much can be learned from

observing the

same astronomical object at many


. Here, the Milky Way.

© 2017 Pearson Education, Inc.Slide37

Summary of Chapter 3

Refracting telescopes make images with a lens.

Reflecting telescopes make images with a mirror.Modern research telescopes are all reflectors.

CCDs are used for data collection.

Data can be formed into images, analyzed


, or used to measure intensity.

Large telescopes gather much more light, allowing study of very faint sources.

Large telescopes also have better resolution.

© 2017 Pearson Education, Inc.Slide38

Summary of Chapter 3, cont.

Resolution of ground-based optical telescopes is limited by atmospheric effects.

Resolution of radio or space-based telescopes is limited by diffraction.Active and adaptive optics can minimize atmospheric effects.

Radio telescopes need large collection area; diffraction is limited.

Interferometry can greatly improve resolution.

© 2017 Pearson Education, Inc.Slide39

Summary of Chapter 3, cont.

Infrared and ultraviolet telescopes are similar to optical.

Ultraviolet telescopes must be above the atmosphere.

X-rays can be focused, but very differently from visible light.

Gamma rays can be detected. This must be done from space.

© 2017 Pearson Education, Inc.